The present invention relates to a new process for the production of substantially closed-cell polyurethane foams.
Processes for producing substantially closed-cell rigid foams containing urethane, urea and biuret groups are generally known.
A review of the production of corresponding rigid foams is given for example in Kunststoff-Handbuch, (Handbook of Plastics), Vol. 7, 1st Edition 1966, edited by R. Vieweg and A. Hochtlen and 2nd Edition 1983, edited by G. Oertel, (Carl Hanser Verlag, Munich).
Rigid foams such as these are normally produced by reacting aromatic polyisocyanates with polyols, preferably polyether polyols or polyester polyols, in the presence of blowing agents, catalysts, and, optionally, auxiliaries and additives.
The fluorochlorohydrocarbons such as R11 that were previously preferably used as blowing agents have been replaced. In particular, these conventional fluorochlorohydrocarbons were replaced due to their ozone-destructive properties, by blowing agents such as, for example, partially halogenated fluorochlorohydrocarbons such as, for example, R141b (1,1,1-dichlorofluoroethane), fluorohydrocarbons, as well as low boiling point alkanes such as, for example, n-pentane, isopentane and cyclopentane.
Rigid polyurethane foams are used, for example, in the production of composite elements or sandwich elements, or in filling cavities in household appliances such as domestic refrigerating equipment, for example, refrigerators or freezers, or insulating storage water heaters.
In the past, the renewable raw material castor oil, a triglyceride widely used in the chemical industry, was used in the production of polyurethanes. Castor oil is suitable for this purpose since it has about three hydroxyl groups per molecule. Castor oil, however, could not previously be used in large amounts (i.e., more than 20 parts by weight of the polyol formulation) in the production of rigid polyurethane foams since its OH number is too low and the resultant rigid foams have an insufficient mechanical stability, particularly in the case of rigid foams having bulk densities below 50 kg/m.sup.3. The use of large amounts of the renewable raw material castor oil in the production of rigid polyurethane foams is, however, of interest for both economic and ecological reasons.
Thus, the object of the invention was to provide a process for the production of rigid polyurethane foams wherein more than 20 parts by weight of castor oil may be present in the polyol formulation, and that yields products which can be used industrially without any problem.
It has now surprisingly been found that these objects can be achieved by using the polyol formulations according to the invention.